DETERMINING THE OPTIMAL STOCKING DENSITY IN LINER PONDS: A CRITICAL FACTOR FOR REDUCING RISKS & MAXIMIZING PRODUCTION EFFICIENCY

DETERMINING THE OPTIMAL STOCKING DENSITY IN LINER PONDS: A CRITICAL FACTOR FOR REDUCING RISKS & MAXIMIZING PRODUCTION EFFICIENCY

Stocking density is one of the most important parameters affecting the performance of whiteleg shrimp farming in liner ponds. Improper density selection can lead to a series of consequences: rapid pollution, oxygen deficiency, unstable water color, increased disease outbreaks, and reduced profitability.
This article analyzes the key factors influencing optimal density, provides recommended stocking density ranges according to system investment levels, seasonality, and management capability, and introduces the oxygen-capacity method—currently used widely in advanced shrimp farming models.

1. The Role of Stocking Density in Liner Ponds

Compared to traditional earthen ponds, liner ponds accumulate organic matter faster, require stronger artificial water flow, and depend heavily on aeration systems. Thus, stocking density directly affects:

• Dissolved oxygen (DO) consumption

• Formation of toxic gases (NH₃, NO₂, H₂S)

• Stability of algae and microbial communities

• Hepatopancreas health and shrimp growth

• Feed conversion ratio (FCR)

• Survival rates and overall economic efficiency

Therefore, determining optimal density must be based on science rather than subjective experience or the trend of “super-high densities.”

2. Factors Affecting Optimal Stocking Density

2.1. Oxygen Supply Capacity of the System

This is the most important determinant. Oxygen demand increases with shrimp biomass, while oxygen supply depends on:

• Number and horsepower of paddlewheel aerators

• Whether bottom aeration/nano oxygen/venturi systems are installed

• Water depth (deeper water decreases oxygen transfer efficiency)

• Stocking density and shrimp size

If oxygen transfer is insufficient, the pond enters a state of “latent hypoxia”—the leading cause of floating shrimp, reduced feeding, white feces disease, hepatopancreas necrosis, and chronic mortality.

2.2. Ability to Process Organic Waste & Uneaten Feed

Liner ponds accumulate organic matter faster than earthen ponds. Microbial and enzyme systems must be strong enough to:

• Break down bottom waste

• Stabilize water color

• Suppress Vibrio proliferation

Ponds with good waste-collection water flow, bottom siphon systems, and robust probiotic programs can tolerate higher stocking densities than ponds operated manually.

2.3. Post-Larvae Quality & Seasonality

• High-quality, disease-free PLs → suitable for medium–high density

• Weak or unknown-origin PLs → reduce density to avoid disease risk

Seasonal impacts:

• Rainy season: lower DO, unstable pH & alkalinity → reduce density by 15–20%

• Dry season: strong sunlight promotes algae growth → must control algae if stocking at high density

2.4. Management Skill of Technicians

Operators must detect and respond quickly to:

• Algae crashes or color loss

• pH and alkalinity fluctuations

• Sudden Vibrio increases

• Shrimp swimming sluggishly or weak response

• Hepatopancreas swelling or shrinkage

• Changes in feces appearance

Farms with experienced technicians can safely raise shrimp at higher densities.

3. Recommended Stocking Density by Investment Level

Table 1. Stocking density by aeration system (per 1,000 m²)

Safety rule: Never stock beyond the aeration capacity of the pond.

4. Negative Impacts of Overstocking

Recent field surveys show that most incidents in shrimp ponds are linked to exceeding the safe density limit, resulting in:

• Rapid nighttime DO drop

• Increase in NH₃, NO₂, H₂S

• Hepatopancreas damage and white feces

• Strong Vibrio outbreaks

• Slow growth, increased FCR

• High mortality and reduced profit

Especially, ponds stocked >250 shrimp/m² without bottom aeration frequently encounter problems at 45–70 days.

5. Calculating Stocking Density Based on Oxygen Capacity (DO Capacity)

This standard is widely used in high-tech shrimp farming worldwide.

Basic formula:

• 1 HP paddlewheel aerator = 1.5 kg O₂/hour theoretical output

• Safe output ≈ 30% of theoretical

Shrimp oxygen consumption:

• 1 g shrimp consumes ~0.2 mg O₂/hour

Example:

A 1,000 m² pond with 8 HP aerators provides:

• Theoretical output: 12 kg O₂/hour

• Safe output (30%): 3.6 kg O₂/hour

At 20 g shrimp:

• 1 shrimp consumes ~4 mg O₂/hour

• Maximum theoretical biomass load ≈ 900,000 shrimp
  (Not including oxygen consumption from feed waste, microbes, algae, toxic gases, nighttime DO drop, etc.)

→ Practical stocking density must be reduced by ~70%: ≈ 270 shrimp/m²

Safe real-world density: 250–300 shrimp/m². Higher than this risks oxygen shortage.

6. Optimal Stocking Density by Model

Table 2. Optimal density by farming model

7. Technical Recommendations

From scientific analysis and field experience:

• Safe – easy to manage: 150–200 shrimp/m²

• Efficient – high profit: 200–250 shrimp/m²

• High density (requires strong technology): 250–350 shrimp/m²

• Super-intensive (>350 shrimp/m²): Only suitable for farms with professional technicians + bottom aeration + continuous nano oxygen systems.

8. Conclusion

The optimal stocking density for liner ponds must be determined based on aeration capacity, organic waste processing ability, seasonality, post-larvae quality, farming model, and operator skill.

A suitable density not only reduces environmental risks but also stabilizes growth, improves FCR, and increases economic efficiency—forming a solid foundation for sustainable liner-pond shrimp farming in Vietnam amid climate change and rising production costs.